Sickle cell disease (SCD) was first recognized because of morphologic abnormalities in red cells. Patients with this genetic disorder produce sickle hemoglobin (Hb S), which tends to polymerize under hypoxic conditions. Consequently, their blood includes many deformed red cells, including so-called irreversibly sickled cells (ISCs). ISCs are dense and rigid, and may occlude capillaries and cause various complications. We believe that elucidating the mechanism of formation of ISCs is very important to understanding this disease. In this project, we will focus on the irreversible deformation of red cells (SS cells) from Hb SS patients using new methods and strategies, and we will study the relationship of irreversible deformation to cell density and patient's clinical condition. Our new approach to the study of irreversible deformation includes the following. First, we will use an image analysis system to quantify the irreversible deformation of SS cells. Most investigators have estimated the population of ISCs by a visual method, using the classic definition of ISCs as cells being at least twice as long as they are wide or being deformed with projections. This results in only two types of cells: "ISC" or not. ISC number, by this definition, is purely dependent on the person performing the measurement. However, the degree of irreversible deformation in SS cells is extremely variable. The numerical values obtained by our image analysis system is a more accurate way to quantify deformation. Second, we will examine factors such as patients Hb F level and genetic factors such as presence of alpha thalassemia and beta thalassemia, and the beta-s haplotypes in relation to the degree of irreversible deformation in SS cells. The degree of irreversible deformation in cells from SCD patients with different genetic backgrounds will be compared statistically in relation to other hematologic factors. Third, we will study longitudinal changes in degree of deformation in SS cells from individual patients. We observed that the degree of deformation in SS cells from some patients (with low Hb F) changes with time, although some studies done by the classic visual method concluded that ISC counts are unchanged in individual patients. Fourth, we will study the shape variation in individual cells; Hb F cells, non-F cells, reticulocytes, and mature cells, in relation to their density. It was reported that hematologic factors and the tendency to form dense cells are heterogeneous among cells even in individual patients. We believe that this new approach to the study of irreversible deformation in SS cells will further the understanding of SCD.